The present invention generally relates to vehicles for laying pipe on uneven or sloped terrain.
A conventional pipeline construction method used in steep mountain terrain is as follows. First, a route is chosen with environmental impact considerations and land acquisitions. The land is cleared and profiled. When the routing of pipeline is up or down a substantial grade such as mountains, the pipeline will run as near perpendicular to grade as possible. This minimizes the possibility of the pipeline being damaged if there is any movement in the ground. An excavator anchored to a bulldozer is used to dig trenches up the steep slopes. The bulldozer winch cable connected to the excavator holds the excavator in position for digging. When the excavator needs repositioning, the bulldozer winch is used to help the excavator climb the grade. Multiple bulldozers may be anchored together if the slope is too long for the length of winch cable on one bulldozer. Pipe sections are then positioned in the trench using a sidewinder bulldozer. The same process used for anchoring excavators on steep grades is used with the sidewinder pipe layers. Only one pipe section can moved up the grade at a time. Once a pipe section is positioned in the trench, the sidewinder must travel back to the bottom of the grade to get the next section. To match the pipe sections to the shape of terrain, they are formed on sight. All pipe sections are coated with a special anticorrosion coating. The coating must be protected from damage. Areas at the ends of the pipe sections near the weld joint are not coated with the protective coating. These areas are coated after the weld and inspection processes are completed. Pipe sections are positioned in the trench on sand bags. The trench is enlarged around the pipe joints to allow access for welding and inspection. Hydrostatic testing is performed after all weld joints have been certified. The trench is backfilled, leveled and seeded once the pipeline has been approved.
Another known prior art method is to employ tree-harvesting vehicles with a platform leveling system. A number of manufacturers (e.g., Komatsu, Cat, John Deere, Tiger Cat, and Timber Pro) build equipment known as Feller Bunchers, with leveling systems, used for harvesting trees. Study of this equipment shows that the maximum tilt angle from front-to-back for these systems is about 20°28° (TimberPro) forward, and less than 10° to the back. This equipment can also tilt side-to-side up from 11° up to 20° (TimberPro). Maintaining a level platform when rotating the load is important, because otherwise the vehicle can tip in a dangerous manner This is especially true when attempting to lay pipe on terrain sloped more than 25° and up to 45°-50°.
Accordingly, there is a need for providing a pipe-laying vehicle having a leveling system, and providing a front-to-back tilt angle, preferably substantially greater than 20-28° forward, such as up to about 45°-50° forward, and up to 5° to the back, and up to 15° to either side.
An angled boom head, i.e., the ability to angle or tilt a boom head having lift cables running through it, would be advantageous for the reasons now provided. Pipe-laying experience in the field shows that it is desirable to use two cables to lift and position the pipe, and to be able to position two different pipe lengths from one location. Using two cables eliminates the need to manually force the pipe to match the grade of the trench. Based on experience with booms and using two cables to lift a load, the load will position itself perpendicular to the centerline of the boom. Depending on the size of the load and the length of the cables, it is sometimes impossible to force a load into a position that is angled to the boom. This creates a significant design challenge, which was solved with the present invention by using a common center for the pivot of the angle boom and the lift cable transfer sheaves. By using the common pivot, there will be little change in the hook height when the angle is changed to aligned the load with the trench. Feller Bunchers do not have an angled boom head.
Other prior art located in a search and cited here shows some ability to angle a boom head, or some ability to level a rotating platform, but no known vehicle combines both functions in the manner of the present invention.
Accordingly, there is a need for a vehicle for laying pipe on hilly or mountainous terrain as described above.